One of the more important tests for determining the production capacity of a hydrocarbon well consists in stopping production by means of a valve and in recording the pressure variations which result from the well being closed. It is advantageous to be able to close the production column in the immediate proximity of the underground production zone so as to eliminate certain disturbing effects due to the compressibility of the fluid present in the production column which effects appear when the well is closed at the surface.
The aim of the invention is to provide a closure tool which is simple in structure, which is capable of being installed in the production column of a well throughout the period that tests are performed on the well, and which can then be removed without difficulty.